It's long been a dream of mankind to put together a map showing the geographic locations of NFL fanbases. The CommonCensus map tried to do it though polling; we took a crack at one based solely on proximity. But all previous efforts have been self-selecting or otherwise flawed. If only there was a massive database of millions of Americans identifying their favorite teams, with precise geographic information included.

• Alaska is confused.
• New England owns New England, and pockets around the country.
• The Jets have just one county—Nassau County, on the western end of Long Island.
• Florida, home of expats, contains pockets of Giants, Patriots, Steelers, Packers, and Bears fans
• The lightly populated Great Plains and Rocky Mountain regions, far from any team, transition from Vikings fandom in the east to Broncos fandom to—unexpectedly—Cowboys fandom in Idaho, Utah, and Nevada.
• Oakland has impressive penetration on the periphery of 49ers country, even into Nevada and Oregon.

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Four more maps, each showing the country's fandom prior to each round of the playoffs, only including the teams still alive. Allegiances remain largely geographical, but Patriots fans gradually spread across the nation like mange. Again, click to enlarge.

One final chart, extracted from the data. If you're a fan of one team, who are your friends most likely to be fans of? Here are the top five most common allegiances for Facebook friends of fans of each team. Once again, geography rules—except for the large numbers of Cowboys, Steelers, and Patriots fans on everybody's list. I'd say that's accurate—nearly all of us know fans of those three teams.